CVE-2021-31859
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIncorrect privileges in the MU55 FlexiSpooler service in YSoft SafeQ 6 6.0.55 allows local user privilege escalation by overwriting the executable file via an alternative data stream.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceThe MU55 FlexiSpooler service in YSoft SafeQ 6 version 6.0.55 runs with elevated Windows service privileges but has incorrect file permissions that allow a low-privileged local user to overwrite the service executable file via a Windows Alternate Data Stream (ADS). This enables local privilege escalation from a standard user to SYSTEM-level access.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 6.0.55CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Verify YSoft SafeQ 6 versionCheck the installed version of YSoft SafeQ on the system using the vendor's standard version detection method or check Add/Remove Programs for 'YSoft SafeQ' version 6.0.55Affected if YSoft SafeQ version 6.0.55 is installed
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Locate FlexiSpooler serviceOpen Windows Services console (services.msc) and search for a service named 'MU55 FlexiSpooler' or 'FlexiSpooler', or run 'sc query' to enumerate services and find one containing 'FlexiSpooler'Affected if The FlexiSpooler service exists on the system
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Identify service executable pathRight-click the FlexiSpooler service, select Properties, and note the path to the executable file shown in 'Path to executable'Affected if The service executable path is identified
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Check NTFS permissions on service executableRight-click the service executable file, select Properties > Security tab, then check the permissions for standard users or the 'Users' group. Specifically verify if Write or Modify permissions are granted to non-admin accountsAffected if Standard non-admin users have Write or Modify permissions to the service executable file
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Test write access via ADSAs a low-privilege standard user (not administrator), attempt to create a Windows Alternate Data Stream on the FlexiSpooler service executable using a command such as 'echo test > "<path to service exe>:test.txt"'Affected if A standard user can successfully create an Alternate Data Stream on the service executable, indicating exploitable permissions
A system is affected if YSoft SafeQ version 6.0.55 is installed with the FlexiSpooler service, and non-administrative users have write permissions to the service executable file.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataApply the vendor patch when available; in the interim, audit and correct NTFS file permissions on the FlexiSpooler service executable to prevent unauthorized modification by non-admin users, and restrict local access to the affected system.
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-31859 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-31859 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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